1. Field of the Invention
The present invention relates to a target position detecting device for detecting a target position on a TV screen or a video projector screen. The device of the present invention is typically used in a computer-controlled gun shooting game machine or a video projector, wherein a target position aimed at by a gun or a position pointed out by a pointer is detected.
2. Description of Prior Art
Shown in FIG. 1 is a computer-controlled gun shooting game machine disclosed in Japanese Laid-Open Patent Publication No. 52(1977)-36900. In this game machine, a gun 2 is pivotally movable in both X-direction (leftward and rightward) and Y-direction (upward and downward) so that a target displayed on a screen 1a of a monitor 1 can be aimed at. The position of the gun 2 aiming at the target is detected by X- and Y-volumes 3, 4 having variable resistors in the interior thereof.
Specifically, the X-directional pivotal motion of the gun 2 is transmitted via rods 9a, 9b to a sector gear 5 with which a pinion gear 7 is meshingly engaged. The rotation of the pinion gear 7 is transmitted via a rod 3a to the X-volume 3. The resistance of the X-volume 3 is varied in accordance with a rotational angle of the rod 3a. On the other hand, the Y-directional pivotal motion of the gun 2 is transmitted via the rod 9a to a sector gear 6 with which a pinion gear 8 is meshingly engaged. The rotation of the pinion gear 8 is transmitted via a rod 4a to the Y-volume 4. The resistance of the Y-volume 4 is varied in accordance with a rotational angle of the rod 4a. With the detection of resistances of or voltages developed across the variable resistors in the X-and Y-volumes, the position of the gun 2 can be identified.
In the above-described game machine, there is a difficulty in performing a positional adjustment of the gun 2 relative to the monitor screen 1a. The positional setting of the sector gear 5 is performed in such a manner that when the gun 1 is in a position aiming at a target displayed at the center of the monitor screen 1a, the X-volume 3 is in the middle of the resistance of the variable resistor. The positional setting of the sector gear 6 is performed in a similar fashion. After such positional settings, the sector gear 6 is fixedly secured to the rod 9a with a nut 10, and the sector gear 5 to the rod 9b with a fastening screw (not shown).
However, with only the above-described procedure, the resistance of the X-volume 3 is usually symmetrically imbalanced when the gun 2 is moved to the leftmost and rightmost positions from the center of the screen 1a. Specifically, the decreased value of the resistance of the X-volume 3 when the gun 2 is moved to aim at the leftmost position on the screen 1a is usually not equal to the increased value of the resistance of the X-volume when the gun is moved to aim at the rightmost position on the screen 1a. This is also true with respect to the resistance of the Y-volume 4. To correct such imbalances, the positional settings are carried out for several times while moving the gun 2 to aim at different positions on the monitor screen 1a. The attachment positions of the sector gears 5, 6 are finally determined when all the conditions are compromised.
In addition to the above-described difficulty, there is another problem in that the target position cannot be detected with high accuracy due to variations in accuracy of the mechanism and in the resistances of the variable resistors used in X- and Y-volumes 3, 4.